Neonatal activation of CD28 signaling overcomes T cell anergy and prevents autoimmune diabetes by an IL-4-dependent mechanism

Islet cell stress induced by insulin-degrading enzyme deficiency promotes regeneration and protection from autoimmune diabetes

Tuning of protein homeostasis through mobilization of the unfolded protein response (UPR) is key to the capacity of pancreatic beta cells to cope with variable demand for insulin. Here, we asked how insulin-degrading enzyme (IDE) affects beta cell adaptation to metabolic and immune stress. C57BL/6 and autoimmune non-obese diabetic (NOD) mice lacking IDE were exposed to proteotoxic, metabolic, and immune stress. IDE deficiency induced a low-level UPR with islet hypertrophy at the steady state, rapamycin-sensitive beta cell proliferation enhanced by proteotoxic stress, and beta cell decompensation upon high-fat feeding. IDE deficiency also enhanced the UPR triggered by proteotoxic stress in human EndoC-βH1 cells. In Ide-/- NOD mice, islet inflammation specifically induced regenerating islet-derived protein 2, a protein attenuating autoimmune inflammation. These findings establish a role of IDE in islet cell protein homeostasis, demonstrate how its absence induces metabolic decompensation despite beta cell proliferation, and UPR-independent islet regeneration in the presence of inflammation.

Pancreatic islet cell stress induced by insulin-degrading enzyme deficiency promotes islet regeneration and protection from autoimmune diabetes

Appropriate tuning of protein homeostasis through mobilization of the unfolded protein response (UPR) is key to the capacity of pancreatic beta cells to cope with highly variable demand for insulin synthesis. An efficient UPR ensures a sufficient beta cell mass and secretory output but can also affect beta cell resilience to autoimmune aggression. The factors regulating protein homeostasis in the face of metabolic and immune challenges are insufficiently understood. We examined beta cell adaptation to stress in mice deficient for insulin-degrading enzyme (IDE), a ubiquitous protease with high affinity for insulin and genetic association with type 2 diabetes. IDE deficiency induced a low-level UPR in both C57BL/6 and autoimmune non-obese diabetic (NOD) mice, associated with rapamycin-sensitive beta cell proliferation strongly enhanced by proteotoxic stress. Moreover, in NOD mice, IDE deficiency protected from spontaneous diabetes and triggered an additional independent pathway, conditional on the presence of islet inflammation but inhibited by proteotoxic stress, highlighted by strong upregulation of regenerating islet-derived protein 2, a protein attenuating autoimmune inflammation. Our findings establish a key role of IDE in islet cell protein homeostasis, identify a link between low-level UPR and proliferation, and reveal an UPR-independent anti-inflammatory islet cell response uncovered in the absence of IDE of potential interest in autoimmune diabetes.

Myeloid-derived suppressor cells exacerbate Sjögren's syndrome by inhibiting Th2 immune responses

Myeloid-derived suppressor cells (MDSCs) can regulate various aspects of immune responses based on their potent immune-suppressive activity. Studies reported that MDSCs participated in many autoimmune diseases. However, the role of MDSCs in Sjögren's syndrome (SS) is unknown. In this study, we determined the frequencies and function of MDSCs in non-obese diabetic (NOD) mice and SS patients. The NOD mice were adoptively transferred with MDSCs or treated with anti-Gr1 antibody. Results showed that peripheral MDSCs increased significantly with the development of SS-like syndrome in NOD mice and the percentage of MDSCs was higher in SS patients than healthy controls. The SS-like syndrome aggravated after transfer of MDSCs in NOD mice. The deletion of MDSCs in NOD mice alleviated SS-like syndrome. Mechanistically, MDSCs down-regulated the percentages of Th2 cells in NOD mice and SS patients. In summary, our findings suggested that MDSCs exacerbated Sjögren's syndrome by inhibiting Th2 cells.

CD28-specific immunomodulating antibodies: what can be learned from experimental models?

Tolerance induction to alloantigens remains a major challenge in transplant immunology. Progress in the last decade of our understanding of T-cell activation has led to the development of new immunotherapeutic strategies to replace conventional immunosuppression which inhibits the immune system in a nonspecific way. In particular, positive and negative costimulatory molecules of the CD28 family have been consistently demonstrated to be critical for the development of productive immune responses as well as the establishment and maintenance of peripheral tolerance. However, recent discoveries of novel costimulatory interactions confer a novel dimension to the immunoregulatory interactions within the B7:CD28 family and compels a revised view within a "quintet" of costimulatory molecules: CD28/B7/CTLA-4/PD-L1/ICOSL. Complexity introduced in this more detailed costimulatory pathway has important implications in therapeutic interventions against human immunological diseases and, especially, highlight the fundamental differences in selectively targeting CD28 molecules instead of B7 counterparts. In this review, we discuss these differences and emphasize different CD28-specific immunomodulating strategies evaluated in experimental models of transplantation and autoimmune diseases.

Effector and naturally occurring regulatory T cells display no abnormalities in activation induced cell death in NOD mice

Background

Disturbed peripheral negative regulation might contribute to evolution of autoimmune insulitis in type 1 diabetes. This study evaluates the sensitivity of naïve/effector (Teff) and regulatory T cells (Treg) to activation-induced cell death mediated by Fas cross-linking in NOD and wild-type mice.

Principal Findings

Both effector (CD25⁻, FoxP3⁻) and suppressor (CD25⁺, FoxP3⁺) CD4⁺ T cells are negatively regulated by Fas cross-linking in mixed splenocyte populations of NOD, wild type mice and FoxP3-GFP tranegenes. Proliferation rates and sensitivity to Fas cross-linking are dissociated in Treg cells: fast cycling induced by IL-2 and CD3/CD28 stimulation improve Treg resistance to Fas-ligand (FasL) in both strains. The effector and suppressor CD4⁺ subsets display balanced sensitivity to negative regulation under baseline conditions, IL-2 and CD3/CD28 stimulation, indicating that stimulation does not perturb immune homeostasis in NOD mice. Effective autocrine apoptosis of diabetogenic cells was evident from delayed onset and reduced incidence of adoptive disease transfer into NOD.SCID by CD4⁺CD25⁻ T cells decorated with FasL protein. Treg resistant to Fas-mediated apoptosis retain suppressive activity in vitro. The only detectable differential response was reduced Teff proliferation and upregulation of CD25 following CD3-activation in NOD mice.

Conclusion

These data document negative regulation of effector and suppressor cells by Fas cross-linking and dissociation between sensitivity to apoptosis and proliferation in stimulated Treg. There is no evidence that perturbed AICD in NOD mice initiates or promotes autoimmune insulitis.

Intrinsic and extrinsic control of peripheral T-cell tolerance by costimulatory molecules of the CD28/ B7 family

Positive and negative costimulation by members of the CD28 family is critical for the development of productive immune responses against foreign pathogens and their proper termination to prevent inflammation-induced tissue damage. In addition, costimulatory signals are critical for the establishment and maintenance of peripheral tolerance. This paradigm has been established in many animal models and has led to the development of immunotherapies targeting costimulation pathways for the treatment of cancer, autoimmune disease, and allograft rejection. During the last decade, the complexity of the biology of costimulatory pathways has greatly increased due to the realization that costimulation does not affect only effector T cells but also influences regulatory T cells and antigen-presenting cells. Thus, costimulation controls T-cell tolerance through both intrinsic and extrinsic pathways. In this review, we discuss the influence of costimulation on intrinsic and extrinsic pathways of peripheral tolerance, with emphasis on members of the CD28 family, CD28, cytotoxic T-lymphocyte antigen-4 (CTLA-4), and programmed death-1 (PD-1), as well as the downstream cytokine interleukin-1 (IL-2).

Monoclonal antibody-induced cytokine-release syndrome

Monoclonal antibodies (mAbs) are widely used in anti-inflammatory and tumor therapy. Although effective, mAbs can cause a variety of adverse effects. An important toxicity seen with a few mAbs is cytokine-release syndrome (CRS). These mAbs include: alemtuzumab, muromonab-CD3, rituximab, tosituzumab, CP-870,893, LO-CD2a/BTI-322 and TGN1412. By contrast, over 30 mAbs used clinically are not associated with CRS. In this review, the clinical aspects of CRS, the mAbs associated with CRS, the cytokines involved and putative mechanisms mediating cytokine release will be discussed. This will be followed by a discussion of the poor predictive value of studies in animals and the prospects for creating in vitro screens. Finally, approaches to decreasing the probability of CRS, decreasing the severity or treating CRS, should it occur, will be described.

A CD1d-dependent antagonist inhibits the activation of invariant NKT cells and prevents development of allergen-induced airway hyperreactivity

The prevalence of asthma continues to increase in westernized countries, and optimal treatment remains a significant therapeutic challenge. Recently, CD1d-restricted invariant NKT (iNKT) cells were found to play a critical role in the induction of airway hyperreactivity (AHR) in animal models and are associated with asthma in humans. To test whether iNKT cell-targeted therapy could be used to treat allergen-induced airway disease, mice were sensitized with OVA and treated with di-palmitoyl-phosphatidyl-ethanolamine polyethylene glycol (DPPE-PEG), a CD1d-binding lipid antagonist. A single dose of DPPE-PEG prevented the development of AHR and pulmonary infiltration of lymphocytes upon OVA challenge, but had no effect on the development of OVA-specific Th2 responses. In addition, DPPE-PEG completely prevented the development of AHR after administration of alpha-galactosylceramide (alpha-GalCer) intranasally. Furthermore, we demonstrate that DPPE-PEG acts as antagonist to alpha-GalCer and competes with alpha-GalCer for binding to CD1d. Finally, we show that DPPE-PEG completely inhibits the alpha-GalCer-induced phosphorylation of ERK tyrosine kinase in iNKT cells, suggesting that DPPE-PEG specifically blocks TCR signaling and thus activation of iNKT cells. Because iNKT cells play a critical role in the development of AHR, the inhibition of iNKT activation by DPPE-PEG suggests a novel approach to treat iNKT cell-mediated diseases such as asthma.

Attenuation of Th1 response through galectin-9 and T-cell Ig mucin 3 interaction inhibits autoimmune diabetes in NOD mice

Galectin-9 (gal-9), widely expressed in many tissues, regulates Th1 cells and induces their apoptosis through its receptor, T-cell Ig mucin 3, which is mainly expressed on terminally differentiated Th1 cells. Type 1 diabetes is a Th1-dominant autoimmune disease that specifically destroys insulin-producing beta cells. To suppress the Th1 immune response in the development of autoimmune diabetes, we overexpressed gal-9 in NOD mice by injection of a plasmid encoding gal-9. Mice treated with gal-9 plasmid were significantly protected from diabetes and showed less severe insulitis compared with controls. Flow cytometric analyses in NOD-T1/2 double transgenic mice showed that Th1-cell population in spleen, pancreatic lymph node and pancreas was markedly decreased in gal-9 plasmid-treated mice, indicating a negative regulatory role of gal-9 in the development of pathogenic Th1 cells. Splenocytes from gal-9 plasmid-treated mice were less responsive to mitogenic stimulation than splenocytes from the control group. However, adoptive transfer of splenocytes from gal-9-treated or control mice caused diabetes in NOD/SCID recipients with similar kinetics, suggesting that gal-9 treatment does not induce active tolerance in NOD mice. We conclude that gal-9 may downregulate Th1 immune response in NOD mice and could be used as a therapeutic target in autoimmune diabetes.

Dysrulation of T cell peripheral tolerance in type 1 diabetes

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease in which the insulin producing beta cells are destroyed. The breakdown of beta cell-specific self-tolerance by T cells involves a number of dysregulated events intrinsic and extrinsic to T cells. Herein, we review the key mechanisms that drive beta cell autoimmunity, with an emphasis on events that influence the expansion and differentiation of pathogenic T cells in the periphery.

CD40 on NOD CD4 T cells contributes to their activation and pathogenicity

Our goals in this study were to investigate conditions under which T cells from NOD mice express CD40 and to determine how CD40 on autoreactive CD4 T cells contributes to their pathogenicity in T1D. Using CD40-positive diabetogenic T cell clones and CD4 T cells from NOD mice, we examined expression of CD40 upon activation through the TCR and costimulation through either CD28 or CD40. Our results indicate that CD40 expression is increased upon activation with antigen/MHC and that activation of NOD CD4 T cells through TCR/CD40 rapidly induced CD40 expression. Furthermore, CD40 costimulation promoted T cell proliferation to the same extent as costimulation through TCR/CD28. Importantly, costimulation of CD4 T cells through CD40 also interfered with T cell homeostasis by altering regulation of CTLA-4 expression. Through CD40-CD154 blocking studies, we demonstrated that signaling between T cells through CD40 and its ligand contributes to activation of pathogenic T cells and that blocking CD40 on T cells abrogates their ability to transfer diabetes. Thus, costimulation through CD40 on NOD T cells contributes to their pathogenicity by providing additional pathways for activation and by inhibiting upregulation of CTLA-4 during T cell activation.

Therapeutic potential of immunostimulatory monoclonal antibodies

The aim of cancer immunotherapy is to employ the specificity of the immune system to provide a more effective, less toxic, treatment compared with conventional therapies. Although many strategies have been used to try to generate effective anticancer immune responses, very few have reached mainstream clinical use. A new approach introduced over the last few years is to use immunostimulatory mAbs (monoclonal antibodies) to boost weak endogenous antitumour immune responses to levels which are therapeutic. Such agonistic or antagonistic mAbs bind to key receptors in the immune system acting to enhance antigen presentation, provide co-stimulation or to counteract immunoregulation. In animal models, this approach has been shown to promote powerful tumour-specific T-cell responses capable of clearing established tumour and leaving the animal with long-term immunity. In addition to this impressive therapy seen in tumour models, these same mAbs also have the potential to be therapeutically useful in autoimmune and infectious diseases. This review discusses the use of these mAbs as therapeutic agents, their advantages and disadvantages and the challenges that need to be overcome to use them clinically.

Systemic expression of heme oxygenase-1 ameliorates type 1 diabetes in NOD mice

Heme oxygenase-1 (HO-1) is an enzyme with potent immunoregulatory capacity. To evaluate the effect of HO-1 on autoimmune diabetes, female NOD mice at 9 weeks of age received a single intravenous injection of a recombinant adeno-associated virus bearing HO-1 gene (AAV-HO-1; 0.5 x 10(10)-2.5 x 10(10) viruses/mouse). In a dose-dependent manner, HO-1 transduction reduced destructive insulitis and the incidence of overt diabetes examined over a 15-week period. HO-1-mediated protection was associated with a lower type 1 T-helper cell (Th1)-mediated response. Adaptive transfer experiments in NOD.scid mice demonstrated that splenocytes isolated from AAV-HO-1-treated mice were less diabetogenic. Flow cytometry analysis revealed no significant difference in the percentages of CD4(+)CD25(+) regulatory T-cells between saline-treated and AAV-HO-1-treated groups. However, the CD11c(+) major histocompatibility complex II(+) dendritic cell population was much lower in the AAV-HO-1-treated group. A similar protective effect against diabetes was observed in NOD mice subjected to carbon monoxide (CO) gas (250 ppm CO for 2 h, twice per week). These data suggest that HO-1 slows the progression to overt diabetes in pre-diabetic NOD mice by downregulating the phenotypic maturity of dendritic cells and Th1 effector function. CO appears to mediate at least partly the beneficial effect of HO-1 in this disease setting.

Enhanced cardiac allograft survival by Vav1-Rac signaling blockade in a mouse model

BACKGROUND

Vav1-Rac signaling plays a pivotal role in TCR/antigen and CD28 signals for T cell activation. However, pharmacological interference of this signaling has not been tested in the prevention of alloimmune-mediated allograft rejection. It has been demonstrated that 6-thio-GTP, a metabolite of azathioprine, specifically inhibits Vav1-Rac activity in T lymphocytes. Here we show the immunosuppressive efficacy of 6-thio-GTP in the prevention of cardiac allograft rejection.

METHODS

T cell proliferations were measured by (3)H-thymidine uptake. The immunosuppressive activities of 6-thio-GTP were tested in the cardiac allograft model of C57BL/6 (H-2(b)) to Balb/c (H-2(d)) mice.

RESULTS

6-Thio-GTP inhibited TCR/alloantigen stimulated T cell proliferation and CD28-dependent T cell survival. Administration of 6-thio-GTP (0.5 mg/kg) prolonged graft survival to 13.8+/-2.39 days compared to 8.3+/-0.48 days in PBS controls (p<0.0001). Combination of 6-thio-GTP (0.5 mg/kg) with CsA (15 mg/kg) enhanced graft survival from 15.0+/-1.61 days in CsA treated recipients to 36.8+/-2.17 days in those received 20 days of combination therapy of CsA and 6-thio-GTP (p<0.0001), or to 42.7+/-16.63 days in the group treated with 20 days of CsA and 60 days of 6-thio-GTP (p<0.0001). Lymphocytes from 6-thio-GTP treated recipients with long-term surviving grafts (>60 days) displayed reduced proliferative response to alloantigen and higher frequencies of regulatory T cells (Treg).

CONCLUSION

Vav1-Rac inhibitor 6-thio-GTP prolongs allograft survival alone or in combination with CsA by suppression of alloreactive T cell activation. Our findings suggest the therapeutic potential of pharmacological interference of Vav1-Rac signaling for transplantation.

Patients with chronic pancreatitis have islet progenitor cells in their ducts, but reversal of overt diabetes in NOD mice by anti-CD3 shows no evidence for islet regeneration

Monoclonal antibodies to T-cell coreceptors have been shown to tolerise autoreactive T-cells and prevent or even reverse autoimmune pathology. In type 1 diabetes, there is a loss of insulin-secreting beta-cells, and a cure for type 1 diabetes would require not only tolerance induction but also recovery of the functional beta-cell mass. Although we have previously shown that diabetic mice have increased numbers of ductal progenitors in the pancreas, there is no evidence of any increase of insulin-secreting cells in the ducts. In contrast, in the adult human pancreas of patients with chronic pancreatitis, we can demonstrate, in the ducts, increased numbers of insulin-containing cells, as well as cells containing other endocrine and exocrine markers. There are also significantly increased numbers of cells expressing the homeodomain protein, pancreatic duodenal homeobox-1. Anti-CD3 has been shown to reverse overt diabetes in NOD mice; thus, we have used this model to ask whether monoclonal antibody-mediated inhibition of ongoing beta-cell destruction enables islet regeneration to occur. We find no evidence that such monoclonal antibody therapy results in either regeneration of insulin-secreting beta-cells or of increased proliferation of islet beta-cells.

CCL4 protects from type 1 diabetes by altering islet beta-cell-targeted inflammatory responses

We previously reported that interleukin (IL)-4 treatment of nonobese diabetic (NOD) mice elevates intrapancreatic CCL4 expression and protects from type 1 diabetes. Here, we show that antibody neutralization of CCL4 abrogates the ability of T-cells from IL-4-treated NOD mice to transfer protection against type 1 diabetes. Intradermal delivery of CCL4 via a plasmid vector stabilized by incorporation of the Epstein-Barr virus EBNA1/oriP episomal maintenance replicon (pHERO8100-CCL4) to NOD mice beginning at later stages of disease progression protects against type 1 diabetes. This protection was associated with a Th2-like response in the spleen and pancreas; decreased recruitment of activated CD8(+) T-cells to islets, accompanied by diminished CCR5 expression on CD8(+) T-cells; and regulatory T-cell activity in the draining pancreatic lymph nodes. Thus, inflammatory responses that target islet beta-cells are suppressed by CCL4, which implicates the use of CCL4 therapeutically to prevent type 1 diabetes.

Impaired vascular function in normoglycemic mice prone to autoimmune diabetes: Role of nitric oxide

Type 1 diabetes is an immuno-inflammatory condition which increases the risk of cardiovascular disease, particularly in young adults. This study investigated whether vascular function is altered in mice prone to autoimmune diabetes and whether the nitric oxide (NO)-cyclic GMP axis is involved. Aortic rings suspended in organ chambers and precontracted with phenylephrine were exposed to cumulative concentrations of acetylcholine. To investigate the role of NO, some experiments were performed in the presence of either 1400W (N-(3-aminomethyl)benzyl-acetamidine hydrochloride), a selective inhibitor of the iNOS-isoform, L-NAME (N(G)-nitro-L-arginine methyl ester hydrochloride), an inhibitor of all three NOS-isoforms, or ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one), a selective inhibitor of guanylate cyclase. Moreover, contractility to phenylephrine, big endothelin-1, and endothelin-1 was assessed and histological analysis and iNOS immunohistochemistry were performed. Endothelium-dependent relaxation was reduced in prediabetic NOD mice (78+/-4 vs. 88+/-2%, respectively, P<0.05 vs. control) despite normal plasma glucose levels (n.s. vs. control). Preincubation with 1400W further attenuated responses in prediabetic (P<0.05 vs. untreated) but not in diabetic or in control mice. In contrast, basal NO bioactivity remained unaffected until the onset of diabetes in NOD mice. Contractile responses to big endothelin-1 and endothelin-1 were reduced in prediabetic animals (P<0.05 vs. control), whereas in diabetic mice only responses to big endothelin-1 were decreased (P<0.05 vs. control). These data demonstrate that endothelium-dependent and -independent vascular function in NOD mice is abnormal already in prediabetes in the absence of structural injury. Early proinflammatory activation due to iNOS in diabetes-prone NOD mice appears to be one of the mechanisms contributing to impaired vasoreactivity.

Manipulation of Regulatory T‐Cell Number and Function with CD28‐Specific Monoclonal Antibodies

Suppressor or "regulatory" CD4 T cells play a key role in the control of autoimmunity and overshooting immune responses to foreign antigens, but can also obstruct effective anticancer therapies. The homeostasis and activation of these regulatory T cells (Treg cells) is tightly connected to that of effector CD4 T cells via the costimulatory receptor CD28 and the cytokine IL-2: Both subsets require costimulation to be activated by antigen, and Treg cells additionally depend on IL-2 produced by effector CD4 T cells in a costimulation-dependent fashion. Depending on the therapeutic aim, blockade, or stimulation of CD28 with monoclonal antibodies (mAb) can therefore profoundly affect the size and activity of the Treg compartment. In this chapter, experiments performed in rodents with distinct types of CD28-specific mAb, and the recent failure to translate CD28-driven Treg activation into humans, are discussed.

The p38 mitogen-activated protein kinase regulates effector functions of primary human CD4 T cells

The role of p38 mitogen-activated protein kinase in primary human T cells is incompletely understood. We analyzed in detail the role of p38 in the regulation of effector functions and differentiation of human CD4 T cells by using a p38-specific inhibitor and a dominant-negative mutant of p38. p38 was found to mediate expression of IL-10 and the Th2 cytokines IL-4, IL-5, and IL-13 in both, primary naive and memory T cells. In contrast, inhibition of p38 activity did not affect expression of the Th1 cytokines IFN-gamma and TNF induced by TCR-stimulation, but decreased IL-12-mediated IFN-gamma expression. Cytokine expression from established Th2 effector cells was also regulated by p38, however, the role of p38 was less pronounced compared to primary CD4 T cells. p38 MAPK regulated cytokine gene expression at both, the transcriptional level by activating gene transcription and the post-transcriptional level by stabilizing cytokine mRNA. As a result of the effect of p38 on IL-4 expression, p38 activity modulated differentiation of naive precursor T cells by inducing a shift of the Th1/Th2 balance toward the immuno-modulatory Th2 direction. Together, the data suggest that p38 plays a key role in human Th2 cell immune responses.

Costimulation and autoimmune diabetes in BB rats

Costimulatory signals regulate T-cell activation. To investigate the role of costimulation in autoimmunity and transplantation, we studied the BB rat model of type 1 diabetes. Diabetes-prone BB (BBDP) rats spontaneously develop disease when 55-120 days of age. We observed that two anti-CD28 monoclonal antibodies (mAb) with different functional activities completely prevented diabetes in BBDP rats. Anti-CD154 mAb delayed diabetes, whereas treatment with CTLA4-Ig or anti-CD80 mAb accelerated disease. Anti-CD86 or anti-CD134L mAbs had no effect. Diabetes resistant BB (BBDR) rats are disease-free, but >95% of them develop diabetes after treatment with polyinosinic-polycytidylic acid and an mAb that depletes Treg cells. In the induced BBDR model, anti-CD154 mAb delayed onset of diabetes, whereas CTLA4-Ig, anti-CD134L or either of the anti-CD28 mAbs had little or no effect. In contrast, blockade of the CD134-CD134L pathway was highly effective for preventing autoimmune recurrence against syngeneic islet grafts in diabetic BBDR hosts. Blockade of the CD40-CD154 pathway was also effective, but less so. These data suggest that the effectiveness of costimulation blockade in the treatment of type 1 diabetes is dependent on both the costimulatory pathway targeted and the mechanism of induction, stage, intensity and duration of the pathogenic process.

Impaired Crkl expression contributes to the defective DNA binding of Stat5b in nonobese diabetic mice

A point mutation in the Stat5b DNA binding domain in the nonobese diabetic (NOD) mouse was shown to have weaker DNA binding compared with the B6 Stat5b. Here, we assessed the binding ability of the mutant Stat5b in the B6 genetic background (B6.NOD-c11) and the wild-type Stat5b in the NOD background (NOD.Lc11). To our surprise, the binding ability of Stat5b is inconsistent with the presence or absence of the Stat5b mutation in these congenic mice but is correlated with the expression levels of the Crkl protein, which was coprecipitated by an anti-Stat5b antibody. Both the expression of Crkl and the Stat5b binding ability are the highest in B6.NOD-c11 and the lowest in NOD while intermediate in B6 and NOD.Lc11 mice. We demonstrated that the adapter molecule Crkl can bind Stat5b and that the Crkl protein is a Stat5b binding cofactor. More importantly, profection of Crkl recombinant protein significantly increased Stat5b binding ability and rescued the binding defect of the NOD mutant Stat5b, suggesting that Crkl is a key regulatory molecule for Stat5b binding. Therefore, the defective Crkl expression may contribute to the development of diabetes in the NOD mice by exacerbating the defective Stat5b binding ability.

Transcriptional regulation of vascular bone morphogenetic protein by endothelin receptors in early autoimmune diabetes mellitus

Endothelin (ET) and bone morphogenic proteins (BMP) have been implicated in the development of micro- and macrovascular complications of type 2 diabetes mellitus due to atherosclerosis. This study investigated vascular BMP-expression during early development of experimental autoimmune diabetes mellitus and whether ET(A) receptors are involved in its regulation, using the selective ET(A) receptor antagonist BSF461314. Specificity of BSF461314 was confirmed through ET-mediated p44/42 mitogen-activated protein kinase (ERK1/2) phosphorylation experiments. For animal studies, non-obese diabetic (NOD) and control mice at 16 weeks of age were treated with BSF461314 for 6 weeks. Plasma glucose levels were measured before and after treatment and vascular gene expression of BMP-2, BMP-7, and BMP-type II receptor was determined in the aorta by quantitative real-time polymerase chain reaction analysis. At the beginning of the study in all animals, plasma glucose levels were within the normal range. After 6 weeks gene expression of vascular BMP-2, BMP-7 and BMP-type II receptor was almost doubled in NOD mice compared with non-diabetic controls (p < 0.05). Concomitant treatment with BSF461314 significantly reduced expression of all BMPs and lowered plasma glucose levels in NOD mice close to controls (all p < 0.05 versus untreated). In conclusion, vascular BMP-2, BMP-7, and BMP-type II receptor expression is upregulated in early stages of autoimmune diabetes mellitus. The data further indicate that ET(A) receptors inhibit diabetes-associated activation of vascular BMPs and regulate plasma glucose levels suggesting that ET(A) receptors might provide a new therapeutic target to interfere with the early development of atherosclerosis in patients with type 1 diabetes mellitus.

Endothelin inhibition delays onset of hyperglycemia and associated vascular injury in type I diabetes: evidence for endothelin release by pancreatic islet beta-cells

This study investigated the role of endothelin-1 for hyperglycemia, vascular, and pancreatic injury in early type I diabetes in non-obese-diabetic (NOD) mice. Endothelium dependent relaxation to acetylcholine and vascular gene expression of endothelin converting enzyme (ECE) isoforms 1 and 2 were studied as indicators of vascular injury. Endothelial NO bioactivity in the aorta was reduced in diabetic NOD mice while vascular expression of ECE-1 and ECE-2 mRNA was increased compared with controls (all p<0.05). Vascular histology was normal in all animals. Unexpectedly, treatment of prediabetic NOD mice for 6 weeks with the orally active ET(A) receptor antagonist BSF461314 prevented onset of diabetes without affecting insulitis severity. ET(A) receptor blockade also restored abnormal endothelial NO bioactivity and reduced ECE-1 and ECE-2 gene expression in NOD mice to levels comparable with healthy controls (p<0.05). Moreover, secretion of endothelin-1 in a time-dependent fashion was observed by pancreatic islet beta-cells cultured in vitro. These data suggest a critical role for ET(A) receptor signaling in the development of autoimmune forms of diabetes and the early vascular injury associated with it.

DNA vaccination with an insulin construct and a chimeric protein binding to both CTLA4 and CD40 ameliorates type 1 diabetes in NOD mice

Type 1 diabetes (T1D), a T-cell-mediated autoimmune disease, could be attributed to many defects in nonobese diabetic (NOD) mice, including deficient expressions of costimulatory molecules that impair antigen presentation. Thus, this deficient antigen presentation may result in a reduced ability to induce a tolerogenic response through negative selection/regulation of autoreactive T cells. Improperly activated T cells seem to be able to induce autoimmune responses causing diabetes. To re-establish tolerance to autoantigens by modulating costimulation, we constructed and tested a new type of DNA vaccine encoding a membrane-bound preproinsulin (mbPPI) and a chimeric gene vector encoding mutant B7.1/CD40L (mB7.1/CD40L) fusion protein. This mutant B7.1 binds CTLA4 but not CD28. We report that young NOD mice immunized with mbPPI along with mB7.1/CD40L DNA vectors significantly reduced diabetes incidence while treatment with CTLA4/IgG1 exacerbated diabetes. In conclusion, the combination of mbPPI and mB7.1/CD40L was able to protect against autoimmunity and diabetes in NOD mice possibly by promoting a more efficient presentation of autoantigen PPI and inducing specific tolerance to PPI by negatively regulating autoreactive T cells.

The NOD mouse: a model of immune dysregulation

Autoimmunity is a complex process that likely results from the summation of multiple defective tolerance mechanisms. The NOD mouse strain is an excellent model of autoimmune disease and an important tool for dissecting tolerance mechanisms. The strength of this mouse strain is that it develops spontaneous autoimmune diabetes, which shares many similarities to autoimmune or type 1a diabetes (T1D) in human subjects, including the presence of pancreas-specific autoantibodies, autoreactive CD4+ and CD8+ T cells, and genetic linkage to disease syntenic to that found in humans. During the past ten years, investigators have used a wide variety of tools to study these mice, including immunological reagents and transgenic and knockout strains; these tools have tremendously enhanced the study of the fundamental disease mechanisms. In addition, investigators have recently developed a number of therapeutic interventions in this animal model that have now been translated into human therapies. In this review, we summarize many of the important features of disease development and progression in the NOD strain, emphasizing the role of central and peripheral tolerance mechanisms that affect diabetes in these mice. The information gained from this highly relevant model of human disease will lead to potential therapies that may alter the development of the disease and its progression in patients with T1D.

Dysregulated B7-1 and B7-2 Expression on Nonobese Diabetic Mouse B Cells Is Associated with Increased T Cell Costimulation and the Development of Insulitis

Little is known about the pathogenic role of B cell dysfunction in T cell-mediated autoimmune disease. We previously reported that B cell hyper-responsiveness, resistance to apoptosis, and accumulation in islets occur during the onset of insulitis, but not in type 1 diabetes (T1D), in NOD mice. In this study we extended these studies to further determine how islet-infiltrated B cells contribute to this inflammatory insulitis. We demonstrate the presence of an increased percentage of B7-1(+) and a decreased percentage of B7-2(+) B cells in the spleen of autoimmune disease-prone NOD and nonobese diabetes-resistant mice compared with the spleen of nonautoimmune disease-prone C57BL/6 and BALB/c mice. An age-dependent differential expression of B7-1 and B7-2 was associated with the development of insulitis and CD4(+)CD25(+) T cell deficiency in autoimmune disease-prone mice. Whereas BCR and LPS stimulation increased B7-2 expression on B cells from autoimmune disease-prone and nonautoimmune disease-prone mice, LPS-induced B7-1 expression was higher on NOD than C57BL/6 B cells. Interestingly, increased expression of B7-1 and B7-2 was found on islet-infiltrated B cells, and this increase was associated with enhanced T cell costimulation. Islet-infiltrated B cells were shown to be a source of TNF-alpha production in islets. B7 blockade of BCR-stimulated NOD B cells by anti-B7-1 and anti-B7-2 mAbs during coadoptive transfer with diabetogenic T cells into NOD.scid mice protected these recipients from T1D. These results suggest that increased B7-1 and B7-2 expression on islet-infiltrated NOD B cells is associated with increased T cell costimulation and the development of inflammatory insulitis in NOD mice.

Perturbed Homeostasis of Peripheral T Cells Elicits Decreased Susceptibility to Anti-CD3-Induced Apoptosis in Prediabetic Nonobese Diabetic Mice

Activation-induced cell death (AICD) plays a key role in the homeostasis of the immune system. Autoreactive T cells are eliminated through AICD both from the thymus and periphery. In this study, we show that NOD peripheral T cells, especially CD8(+) T cells, display a decreased susceptibility to anti-CD3-induced AICD in vivo compared with T cells from diabetes-resistant B6, nonobese diabetes-resistant, and NOD.B6Idd4 mice. The susceptibility of NOD CD8(+) T cells to AICD varies in an age- and dose-dependent manner upon stimulation in vivo with either a mitogenic or nonmitogenic anti-CD3. NOD T cells preactivated by anti-CD3 in vivo are less susceptible than B6 T cells to TCR-induced AICD. Treatment of NOD mice with a mitogenic anti-CD3 depletes CD4(+)CD25(-)CD62L(+) but not CD4(+)CD25(+)CD62L(+) T cells, thereby resulting in an increase of the latter subset in the spleen. Treatment with a nonmitogenic anti-CD3 mAb delays the onset of T1D in 8.3 TCR transgenic NOD mice. These results demonstrate that the capacity of anti-CD3 to protect NOD mice from T1D correlates with its ability to perturb T cell homeostasis by inducing CD8(+) T cell AICD and increasing the number of CD4(+)CD25(+)CD62L(+) T cells in the periphery.

Co-stimulation agonists as a new immunotherapy for autoimmune diseases

Lymphocytes are important in the pathogenesis of many autoimmune diseases. Blocking co-stimulatory signals for T-cell activation has been widely used as an approach to treating autoimmunity, but it has encountered limited clinical success. Some agonistic monoclonal antibodies to co-stimulatory molecules greatly enhance immune responses mediated by T cells, such as antiviral, anti-tumor and alloresponses. Surprisingly, recent studies have demonstrated that these agonists have profound therapeutic effects on autoimmune diseases by potentially depleting autoreactive lymphocytes or by inhibiting their function. These findings imply that signaling through co-stimulatory molecules can have diametric outcomes in modulating immune responses, thereby providing a novel approach to the treatment of autoimmune diseases.

Deficient activation and resistance to activation-induced apoptosis of CD8+ T cells is associated with defective peripheral tolerance in nonobese diabetic mice

Activation-induced cell death (AICD) is a mechanism of homeostasis that limits the clonal expansion of autoreactive T cells and regulates central and peripheral tolerance. In nonobese diabetic (NOD) mice, defects in central and peripheral tolerance are associated with a proliferative hyporesponsiveness of thymocytes and peripheral T cells elicited upon TCR activation. We investigated whether these defects in tolerance induction and hyporesponsiveness of NOD T cells manifest in an altered susceptibility to TCR-induced AICD. TCR-activated NOD splenic CD4+ and CD8+ T cells are more resistant to AICD than control strain C57BL/6, BALB/c, and NOR T cells. NOR CD4+ but not CD8+ T cells are resistant to TCR-induced AICD. Whereas c-FLIP expression is reduced in activated T cells from control strains, it persists in activated NOD CD8+ T cells and is accompanied by diminished activity of caspase-3 and -8. IL-4 reduces this c-FLIP expression and increases caspase-3 and -8 activity in activated NOD CD8+ T cells. Moreover, IL-4 and CD28 costimulation restores the susceptibility of NOD CD8+ T cells to AICD, and this is associated with increased expression of CD25, CD95, CD95L, and TNFR2. Thus, deficient activation of CD8+ T cells and their greater resistance to TCR-induced AICD may mediate defective peripheral tolerance and the development of T1D in NOD mice.

Increased nonobese diabetic Th1:Th2 (IFN-gamma:IL-4) ratio is CD4+ T cell intrinsic and independent of APC genetic background

Autoreactive CD4(+) T cells play a major role in the pathogenesis of autoimmune diabetes in nonobese diabetic (NOD) mice. We recently showed that the non-MHC genetic background controlled enhanced entry into the IFN-gamma pathway by NOD vs B6.G7 T cells. In this study, we demonstrate that increased IFN-gamma, decreased IL-4, and decreased IL-10 production in NOD T cells is CD4 T cell intrinsic. NOD CD4(+) T cells purified and stimulated with anti-CD3/anti-CD28 Abs generated greater IFN-gamma, less IL-4, and less IL-10 than B6.G7 CD4(+) T cells. The same results were obtained in purified NOD.H2(b) vs B6 CD4(+) T cells, demonstrating that the non-MHC NOD genetic background controlled the cytokine phenotype. Moreover, the increased IFN-gamma:IL-4 cytokine ratio was independent of the genetic background of APCs, since NOD CD4(+) T cells generated increased IFN-gamma and decreased IL-4 compared with B6.G7 CD4(+) T cells, regardless of whether they were stimulated with NOD or B6.G7 APCs. Cell cycle analysis showed that the cytokine differences were not due to cycle/proliferative differences between NOD and B6.G7, since stimulated CD4(+) T cells from both strains showed quantitatively identical entry into subsequent cell divisions (shown by CFSE staining), although NOD cells showed greater numbers of IFN-gamma-positive cells with each subsequent cell division. Moreover, 7-aminoactinomycin D and 5-bromo-2'-deoxyuridine analysis showed indistinguishable entry into G(0)/G(1), S, and G(2)/M phases of the cell cycle for both NOD and B6.G7 CD4(+) cells, with both strains generating IFN-gamma predominantly in the S phase. Therefore, the NOD cytokine effector phenotype is CD4(+) T cell intrinsic, genetically controlled, and independent of cell cycle machinery.

Cutting edge: targeted ligation of CTLA-4 in vivo by membrane-bound anti-CTLA-4 antibody prevents rejection of allogeneic cells

Natural engagement of CTLA-4 on host B7 limits T cell activation. We hypothesized that therapeutic cross-linking of CTLA-4 in vivo may further inhibit T cell function and prevent allograft rejection. However, none of the currently available CTLA-4-binding reagents have ligating properties when injected in vivo. The observation that surface-immobilized anti-CTLA-4 mAb inhibits T cell activation in vitro prompted us to develop a membrane-bound single-chain anti-CTLA-4 Ab (7M). To model whether tissue expression of 7M could suppress allograft rejection, we examined the ability of H-2L(d)-specific TCR-transgenic T cells to reject 7M-expressing allogeneic tumor cells injected s.c. Expression of 7M significantly inhibited allogeneic rejection in mice that received CTLA-4(+/+) but not CTLA-4(-/-) T cells. Furthermore, CTLA-4(+/+) T cells that had encountered 7M-expressing tumors in vivo acquired defects in cytokine production and cytotoxicity. Thus, deliberate ligation of CTLA-4 in vivo potently inhibits allogeneic T cell responses.

Regulatory natural killer T cells protect against spontaneous and recurrent type 1 diabetes

Autoimmune diseases, especially type 1 diabetes (T1D), may be caused by dysregulation of the immune system, which leads to hyporesponsiveness of regulatory T helper 2 (Th2) cells and promotion of autoimmune Th1 cells. Natural killer T (NKT) cells, which comprise a minor subpopulation of T cells, play a critical role in immunoregulation as a result of a rapid burst of IL-4 and IFN-gamma secretion. These cells are functionally and numerically deficient in individuals at risk of T1D, as well as in nonobese diabetic (NOD) mice. It is conceivable that protection from T1D may be achieved by correction of this deficiency. Alpha-galactosylceramide (alpha-GalCer) specifically binds to NKT cells in a CD1-dependent manner and stimulates these cells to proliferate and to produce various cytokines, including IFN-gamma, IL-4, and IL-10. In this review, we present evidence that a multiple-dose alpha-GalCer treatment regimen, which is known to promote a dominant Th2 environment, can prevent the onset of spontaneous and cyclophosphamide (CY)-accelerated T1D. This protection is associated with elevated IL-4 and IL-10 in the spleen and pancreas of protected female NOD mice. Concomitantly, IFN-gamma levels are reduced in both tissues. More importantly, the protective effect of gamma-GalCer in CY-accelerated T1D is abrogated by the in vivo blockade of IL-10 activity. We also show that alpha-GalCer treatment significantly prolongs syngeneic islet graft survival in recipient diabetic NOD mice. These findings raise the possibility that alpha-GalCer treatment may be used therapeutically to prevent the onset and recurrence of human T1D.

CD28 function: a balance of costimulatory and regulatory signals

Both the recognition of MHC/antigen complex by the T-cell receptor and engagement of costimulatory molecules are necessary for efficient T-cell activation. CD28 has been widely recognized as the major costimulation pathway for naive T-cell activation, and the CD28/B7 pathway plays a central role in immune responses against pathogens, autoimmune diseases, and graft rejection. In this review, we will summarize evidence that CD28 is also prominent in the regulation of immune responses and the maintenance of peripheral tolerance. Indeed, CD28 engagement increases the expression of the down-modulatory molecule CTLA-4, induces the differentiation of Th2 cells that have a protective function in autoimmunity, and has an obligatory role in the homeostasis of regulatory T cells. Therefore, CD28/B7 interactions induce a balance of costimulatory and regulatory signals that have opposite outcomes on immune responses. This new perspective on CD28 function suggests that caution should be taken in the development of immunotherapies targeting costimulatory pathways.

Immunotherapy of type 1 diabetes: lessons for other autoimmune diseases

The nonobese diabetic (NOD) mouse is a well-recognised animal model of spontaneous autoimmune insulin-dependent diabetes mellitus. The disease is T-cell mediated, involving both CD4 and CD8 cells. Its progress is controlled by a variety of regulatory T cells. An unprecedented number of immunological treatments have been assessed in this mouse strain. This chapter systematically reviews most of these therapeutic manoeuvres, discussing them in the context of their significance with regard to the underlying mechanisms and the potential clinical applications. The contrast between the surprisingly high rate of success found for a multitude of treatments (more than 160) administered early in the natural history of the disease and the few treatments active at a late stage is discussed in depth. Most of the concepts and strategies derived from this model apply to other autoimmune diseases, for which no such diversified data are available.

Congenic mapping of the diabetogenic locus Idd4 to a 5.2-cM region of chromosome 11 in NOD mice: identification of two potential candidate subloci

Twenty diabetes susceptibility loci on 12 mouse chromosomes have been identified to control the development of type 1 diabetes at the level of either initiation of insulitis or progression from insulitis to overt diabetes or both. Previously, we demonstrated that the genetic control of T-cell proliferative unresponsiveness in nonobese diabetic (NOD) mice is linked to Idd4 on mouse chromosome 11. Here, we show by congenic mapping of three newly generated NOD.B6Idd4 diabetes-resistant mouse strains that Idd4 is limited to a 5.2-cM interval of chromosome 11. This B6-derived region expressed in NOD.B6Idd4A mice maps between the D11Nds1 (43.8 cM) and D11Mit38/D11Mit325 (49.0 cM) markers and dramatically reduces the development of both insulitis and type 1 diabetes. NOD.B6Idd4B and NOD.B6Idd4C mice, which carry a smaller B6-derived segment of chromosome 11 that spans <5.2 cM distal to D11Nds1, exhibit protection against type 1 diabetes with the restoration of T-cell proliferation. Our findings suggest that diabetes resistance conferred by Idd4 may be mediated by the Idd4.1 and Idd4.2 subloci. Idd4.1 is localized in the D11Nds1 interval that influences both diabetes and insulitis. Idd4.2 is localized within the D11Mit38/325 interval that mainly influences diabetes incidence and restores T-cell proliferative responsiveness. Three potential candidate genes, platelet activating factor acetylhydrolase Ib1, nitric oxide synthase-2, and CC chemokine genes, are localized in the 5.2-cM interval.

Adeno-associated virus vector-mediated IL-10 gene delivery prevents type 1 diabetes in NOD mice

The development of spontaneous autoimmune diabetes in nonobese diabetic (NOD) mice provides for their use as a model of human type 1 diabetes. To test the feasibility of muscle-directed gene therapy to prevent type 1 diabetes, we developed recombinant adeno-associated virus (rAAV) vectors containing murine cDNAs for immunomodulatory cytokines IL-4 or IL-10. Skeletal muscle transduction of female NOD mice with IL-10, but not IL-4, completely abrogated diabetes. rAAV-IL-10 transduction attenuated the production of insulin autoantibodies, quantitatively reduced pancreatic insulitis, maintained islet insulin content, and altered splenocyte cytokine responses to mitogenic stimulation. The beneficial effects were host specific, as adoptive transfer of splenocytes from rAAV IL-10-treated animals rapidly imparted diabetes in naive hosts, and the cells contained no protective immunomodulatory capacity, as defined through adoptive cotransfer analyses. These results indicate the utility for rAAV, a vector with advantages for therapeutic gene delivery, to transfer immunoregulatory cytokines capable of preventing type 1 diabetes. In addition, these studies provide foundational support for the concept of using immunoregulatory agents delivered by rAAV to modulate a variety of disorders associated with deleterious immune responses, including allergic reactions, transplantation rejection, immunodeficiencies, and autoimmune disorders.

A defect in central tolerance in NOD mice

The predisposition of nonobese diabetic (NOD) mice to develop autoimmune disease is usually attributed to defects in peripheral tolerance mechanisms. Here, evidence is presented that NOD mice display a defect in central tolerance (negative selection) of thymocytes. Impaired central tolerance in NOD mice was most prominent in a population of semi-mature thymocytes found in the medulla. The defect was apparent in vivo as well as in vitro, was independent of IAbetag7 expression and affected both Fas-dependent and Fas-independent pathways of apoptosis; for Fas-dependent apoptosis, the defective tolerance of NOD thymocytes correlated with the strong T cell receptor-mediated up-regulation of caspase 8-homologous FLICE (Fas-associated death-domain-like interleukin 1beta-converting enzyme)-inhibitory protein. In light of these findings, disease onset in NOD mice may reflect defects in central as well as peripheral tolerance.

Tolerogenic strategies to halt or prevent type 1 diabetes

A variety of therapeutic strategies have been developed to tolerize autoreactive T cells and prevent autoimmune pathology. In terms of type 1 diabetes, prevention strategies can inhibit the priming and expansion of autoreactive T cells; however, a cure for diabetes would require tolerance to be established in the presence of primed effector cells together with replacement of the destroyed beta cell mass. Replacement of beta cells could be accomplished by transplantation of islets or stem cells or through islet regeneration. We will focus here on tolerogenic strategies that have been used to prevent onset of type 1 diabetes and discuss the potential for a cure.

Dominant role of intercellular adhesion molecule-1 in the pathogenesis of autoimmune diabetes in non-obese diabetic mice

Intercellular adhesion molecule (ICAM)-1 is involved in forming the immunological synapse. The contribution of ICAM-1 to immune responses is not critical because mice with a disrupted ICAM-1 gene do not have grossly abnormal immune reactivity. Here we report on the surprising finding that diabetes-prone NOD mice with a disrupted ICAM-1 gene (ICAM-1(-/-)) are completely protected from disease development. While 64% of ICAM-1(+/+) and 44% of ICAM-1(+/-) female NOD mice developed overt diabetes until 310 days old, no ICAM-1(-/-) NOD mice became hyperglycaemic. Histological examinations revealed minor infiltration around pancreatic islets of ICAM1(-/-) NOD mice. Administration of cyclophosphamide caused a progression to severe islet destruction in ICAM-1(+/+) NOD mice within 10 days. In contrast, ICAM-1(-/-) mice showed only mild insulitis. Furthermore, ICAM-1(+/+) NOD mice showed an increase of IFN-gamma, interleukin (IL)-12p40 and IL-12p35 pancreatic mRNA levels, leading to an increased ratio of IFN-gamma: IL-4 and IL-12p40: IL-12p35 expression. In contrast, ICAM-1(-/-) NOD mice did not upregulate IFN-gamma or IL-12p40 gene expression but maintained IL-4 and increased IL-12p35 gene expression. These results identify a dominant and non-redundant role of ICAM-1 in the development of autoimmune diabetes.

Complexities of CD28/B7: CTLA-4 costimulatory pathways in autoimmunity and transplantation

Recent advances in the understanding of T cell activation have led to new therapeutic approaches in the treatment of immunological disorders. One attractive target of intervention has been the blockade of T cell costimulatory pathways, which result in more selective effects on only those T cells that have encountered specific antigen. In fact, in some instances, costimulatory pathway antagonists can induce antigen-specific tolerance that prevents the progression of autoimmune diseases and organ graft rejection. In this review, we summarize the current understanding of these complex costimulatory pathways including the individual roles of the CD28, CTLA-4, B7-1 (CD80), and B7-2 (CD86) molecules. We present evidence that suggests that multiple mechanisms contribute to CD28/B7-mediated T cell costimulation in disease settings that include expansion of activated pathogenic T cells, differentiation of Th1/Th2 cells, and the migration of T cells into target tissues. Additionally, the negative regulatory role of CTLA-4 in autoimmune diseases and graft rejection supports a dynamic but complex process of immune regulation that is prominent in the control of self-reactivity. This is most apparent in regulation of the CD4(+)CD25(+)CTLA-4(+) immunoregulatory T cells that control multiple autoimmune diseases. The implications of these complexities and the potential for use of these therapies in clinical immune intervention are discussed.

Interference with CD28, CD80, CD86 or CD152 in collagen-induced arthritis. Limited role of IFN-gamma in anti-B7-mediated suppression of disease

We have investigated interference with co-stimulation by administering mAbs towards CD28, CD80, CD86, and CD152 in mice immunized for the development of collagen-induced arthritis (CIA). Anti-CD80 and anti-CD86 treatment inhibited disease score and incidence, whereas anti-CD28 treatment led only to a delayed disease onset. Administration of anti-CD152 had no effect. The CII-specific Ab-response was suppressed by the co-stimulatory blockade, with a stronger effect on IgG1 than on IgG2a. The CII-driven T cell proliferation, on the other hand, was not affected. Furthermore, T cells primed in the presence of either anti-B7 or anti-CD28 produced markedly increased amounts of IFN-gamma in response to CII. To investigate whether this increase in IFN-gamma was related to disease suppression, IFN-gamma-deficient mice were immunized with CII, treated with anti-B7 and followed for the development of arthritis. As in the wild-type mice, administration of anti-B7 to IFN-gamma-deficient mice led to a reduced disease incidence and severity as well as reduced anti-CII IgG titers. Collectively, these data stress the importance of co-stimulation for the delivery of B cell help rather than for production of Th1 cytokines. We also demonstrate that the enhanced production of IFN-gamma observed after B7-blockade is not accountable for the anti-B7 mediated inhibition of CIA.

Defective CD8+ T cell peripheral tolerance in nonobese diabetic mice

Nonobese diabetic (NOD) mice develop spontaneous autoimmune diabetes that involves participation of both CD4+ and CD8+ T cells. Previous studies have demonstrated spontaneous reactivity to self-Ags within the CD4+ T cell compartment in this strain. Whether CD8+ T cells in NOD mice achieve and maintain tolerance to self-Ags has not previously been evaluated. To investigate this issue, we have assessed the extent of tolerance to a model pancreatic Ag, the hemagglutinin (HA) molecule of influenza virus, that is transgenically expressed by pancreatic islet beta cells in InsHA mice. Previous studies have demonstrated that BALB/c and B10.D2 mice that express this transgene exhibit tolerance of HA and retain only low-avidity CD8+ T cells specific for the dominant peptide epitope of HA. In this study, we present data that demonstrate a deficiency in peripheral tolerance within the CD8+ T cell repertoire of NOD-InsHA mice. CD8+ T cells can be obtained from NOD-InsHA mice that exhibit high avidity for HA, as measured by tetramer (K(d)HA) binding and dose titration analysis. Significantly, these autoreactive CD8+ T cells can cause diabetes very rapidly upon adoptive transfer into NOD-InsHA recipient mice. The data presented demonstrate a retention in the repertoire of CD8+ T cells with high avidity for islet Ags that could contribute to autoimmune diabetes in NOD mice.

Immunotherapy with nondepleting anti-CD4 monoclonal antibodies but not CD28 antagonists protects islet graft in spontaneously diabetic nod mice from autoimmune destruction and allogeneic and xenogeneic graft rejection

BACKGROUND

T-cell activation and the subsequent induction of effector functions require not only the recognition of antigen peptides bound to MHC molecules by T-cell receptor (TCR) for antigen but also a costimulatory signal provided by antigen presenting cells. CD4 T-cell activation and function require the CD4 molecule as a coreceptor of TCR. The CD28/B7 pathway is a major costimulatory signal for T-cell activation and differentiation.

METHODS

The effect of targeting CD4 by nondepleting anti-CD4 monoclonal antibodies (mAbs) versus blocking CD28/B7 by CTLA4Ig, anti-CD80 mAbs, and anti-CD86 mAbs on the prevention of recurrence of autoimmune diabetes after MHC-matched nonobese diabetes-resistant (NOR) islet transplantation in nonobese diabetic (NOD) mice were compared. Whether nondepleting anti-CD4 mAbs prolong allogeneic islet graft survival and xenogeneic pig islet graft survival in diabetic NOD mice were studied. Furthermore, the effect of nondepleting anti-CD4 mAbs combined with CTLA4Ig on allogeneic islet graft survival in NOD mice was investigated.

RESULTS

Recurrence of autoimmune diabetes can be prevented by nondepleting anti-CD4 mAbs. Blocking the CD28/B7 costimulatory pathway by CTLA4Ig or by anti-CD80 mAbs and anti-CD86 mAbs cannot prevent recurrence of autoimmune diabetes after islet transplantation. Short-term treatment with nondepleting anti-CD4 mAbs significantly prolongs allogeneic islet graft survival and xenogeneic pig islet graft survival in diabetic NOD mice. But nondepleting anti-CD4 mAbs combined with CTLA4Ig decreased allogeneic islet graft survival.

CONCLUSIONS

Nondepleting anti-CD4 mAbs but not CD28 antagonists protect islet grafts in diabetic NOD mice from autoimmune destruction and allogeneic and xenogeneic graft rejection. The efficacy of nondepleting anti-CD4 mAbs is compromised when it combines with CTLA4Ig.

CD28 co-stimulation restores T cell responsiveness in NOD mice by overcoming deficiencies in Rac-1/p38 mitogen-activated protein kinase signaling and IL-2 and IL-4 gene transcription

Previously, we reported that T cell hyporesponsiveness induced by TCR ligation is causal to autoimmune diabetes in NOD mice. Neonatal CD28 co-stimulation reverses T cell hyporesponsiveness and protects NOD mice from diabetes by an IL-4-mediated mechanism, indicating that a deficiency in TCR signaling may be overcome by CD28/B7-2 co-stimulation in NOD T cells. To investigate which co-stimulation-induced signaling events mediate this protection, we analyzed the activity of Ras, Rac-1, mitogen-activated protein kinases (MAPK) and several transcription factors in TCR-activated NOD T cells in the presence or absence of CD28 co-stimulation. We show that CD28 co-stimulation restores normal TCR-induced activation of Rac-1 and p38 MAPK in NOD T cells. Deficiencies in TCR-induced nuclear expression of activating protein (AP)-1 binding proteins as well as activation of AP-1 and NF-AT in the IL-2 and IL-4 P1 promoters are also corrected by CD28 co-stimulation. Thus, CD28 co-stimulation reverses NOD T cell hyporesponsiveness by restoring TCR signaling leading to the activation of AP-1 and NF-AT during IL-2 and IL-4 gene transcription. Our findings provide additional evidence that CD28 co-stimulation amplifies signals delivered by the TCR and further explain the mechanism by which CD28 co-stimulation may protect against autoimmune diabetes.

Comparison of a T cell clone and of T cells from a TCR transgenic mouse: TCR transgenic T cells specific for self-antigen are atypical

It has been widely assumed that T cells from TCR-transgenic (Tg) mice better represent the behavior of T cells from normal mice than do in vitro cultures of T cell clones. We have found that autoreactive T cells arising in the presumably more physiological environment of the BDC-2.5 TCR-Tg mouse, despite being apparently "naive" in surface phenotype, are highly activated functionally and do not resemble CD4(+) T cells from a spontaneously diabetic nonobese diabetic (NOD) mouse or the NOD-derived, diabetogenic CD4(+) T cell clone of origin, BDC-2.5. Our results suggest that autoreactive T cells cloned from the spontaneously diabetic NOD mouse more closely resemble effector T cells arising during the natural disease process.